The heating may be implemented by using the convection principle in which the heat is conducted to the press belts, and from them onwards to the product. High-frequency heating (RF, HF) is also commonly used, where the wave-energy created by the heating device is led directly to the product for achieving a dielectric heating effect.
A continuous press is structurally expensive and demanding in terms of directing the heating.
A synchronous press providing a reasonable production capacity must be long, which is structurally demanding. Furthermore, it requires a stacking device having a length of at least one compression length of the product to be pressed.
Different operational problems have also been associated with the available equipments. Heat transfer from the surface to the interior is slow with devices operating according to the convection principle. Increasing the transfer rate of the temperature gradient by raising the surface temperature includes its own problems such as a sudden evaporation of water in wood material and the adhesive. On the other hand, in high-frequency heating the product is heated substantially uniformly in the depth direction, but problems due to sudden local evaporation of water have occurred also in this heating method. Primarily it is specifically the adhesion point that might snap open when releasing compression too early.
For each operation cycle the leading end of the product has to wait for rather a long period in a stacking device preceding a synchronous press having a long construction, at which time the behavior of the adhesive may cause problems, such as absorption, pre-mature curing etc.